1. Field of the Invention
The present invention relates to radio frequency identification (RFID) interrogators and transponders, and more particularly, to an apparatus and method for RFID transponder data encoding.
2. Description of Related Art
In the automatic data identification industry, the use of RFID transponders (also known as RFID tags) has grown in prominence as a way to track data regarding an object to which the RFID transponder is affixed. An RFID transponder generally includes a semiconductor memory in which digital information may be stored, such as an electrically erasable, programmable read-only memory (EEPROMs) or similar electronic memory device. Under a technique referred to as “backscatter modulation,” the RFID transponders transmit stored data by reflecting varying amounts of an electromagnetic field provided by an RFID interrogator by modifying their antenna matching impedances. The RFID transponders can therefore operate independently of the frequency of the energizing field, and as a result, the interrogator may operate at multiple frequencies so as to avoid radio frequency (RF) interference, such as utilizing frequency hopping spread spectrum modulation techniques. The RFID transponders may either be passive, in which they extract their power from the electromagnetic field provided by the interrogator, or active, in which they include their own power source.
Because RFID transponders do not include a radio transceiver, they can be manufactured in very small, light weight and inexpensive units. Passive RFID transponders are particularly cost effective because they lack a power source. In view of these advantages, RFID transponders can be used in many types of applications in which it is desirable to track information regarding a moving or inaccessible object. One such application is to affix RFID transponders to work pieces moving along a conveyor belt of an assembly line. The RFID transponders would contain stored information regarding the particular assembly requirements for the work piece to enable automated equipment to operate on the work piece and perform certain tasks particular to the unique work piece requirements. This way, products having different assembly requirements can be sent down the same assembly line without having to modify the assembly line for each unique requirement. Other applications for RFID technology include asset and inventory control, access control, security, and transportation applications such as vehicle toll collection, parking, and fleet management.
A drawback of conventional RFID systems is that the RFID transponder has limited memory capacity. Data is either encoded as a numeric equivalent of bits or encoded as Full ASCII (American Standard Code for Information Interchange) bytes with 8 bits to a character. Currently, there is no method of compacting variable data or adding functionality to the encoded data.
Another drawback is that errors in the data are sometimes encountered. Static electricity, cosmic radiation, and magnetic or electric fields, to name but a few reasons may cause errors. Currently, there is no method available to detect errors except by comparing data encoded on the tag to the original data. There is also no method available to correct data except by manual methods. In other words, there is no error detection or correction for the stored information within the RFID transponder. Error detection refers to a coding scheme that determines the presence of errors within the data while error correction refers to a coding scheme that corrects an error detected within the data. These coding schemes are referred to as source encoding because they operate upon the original or source data to produce an encoded message for transmission.
A conventional RFID system includes a RFID transponder programmer, a RFID transponder, and a RFID interrogator. The RFID transponder programmer performs the function of programming or writing the data to the RFID transponder. The RFID interrogator performs the function of communicating with the tags and facilitating data transfer. The RFID interrogator may also perform the functions of the RFID transponder programmer and write to the RFID transponder. Known coding schemes, such as Manchester coding or FMO coding, may be employed to communicate between the RFID transponder and the RFID interrogator (or RFID transponder programmer). This application of coding schemes to facilitate effective channel transmission of the data to and from the RFID transponder is referred to as channel encoding. Channel encoding is designed to overcome noise, interference, and distortion caused by the communication channel; however, channel encoding does not protect against errors in the data stored within the RFID transponder. For example, the data within the RFID transponder may become corrupted due to damage to the RFID transponder, electroinagnetic interference, internal electrical circuit or memory failure, etc. The RFID interrogator will correctly read the corrupted data contained within the RFID transponder, but will be unable to discern that the data contains errors. Thus, while transmission checking exists for the read and write process for RFID transponders, there is currently no method to verify that the data contained within a RFID transponder is correct. Consequently, there is no independent or “out-of-channel” verification that the original data traveling through the read/write process arrives at a destination in a fashion identical to its origin.
Accordingly, it would be desirable to provide an apparatus and method for RFID transponder data encoding that would encode variable data more efficiently and provide enhanced functionality to the data encoded in the RFID transponder. The data may be encoded in other than straight Full ASCII bytes. The data may also be encoded to provide error detection and correction. The error detection and correction method would provide source data encoding/decoding to provide data checking and correcting capability to insure data integrity and to improve RFID system performance in the event of data corruption. The method would allow faster “read rates” for increased RFID system performance. The method would be capable of utilizing currently employed symbology checking and correcting algorithms and provide specific schemes to optimize source encoding capability for a given RFID transponder data content and system architecture. Furthermore, an apparatus would be desirable that could utilize such methods and may also combine such features within a bar code reader or a bar code printer. This would allow multiple applications to be supported within one apparatus and existing data encodation and error detection and correction codes from bar code symbology algorithms could be adapted for use with RFID transponders.